The invention relates to a method of supplying connecting elements to a processing apparatus, in which the connecting elements are placed in readiness by a supplying apparatus and individually conveyed to a loading device arranged on the processing apparatus. The invention relates further to a device for supply of connecting elements to a processing apparatus having a supply device for placing connecting elements in readiness, a loading device arranged on the processing apparatus and a conveyor passage connecting the supply unit to the loading device.
The mechanical automatic processing of connecting elements, for example the setting of rivets, the tightening of screws or the welding on of studs, requires a rapid and reliable supply of the connecting elements to the processing apparatus. Any interference with the supply leads to a retardation of the production process and sometimes to costly maintenance operations, and therefore causes considerable costs. A rapid supply of connecting elements suffers, in many applications, from the circumstance that the processing apparatus, whether stationary or guided by a robot, is in a production cell, while the supply apparatus with individuation and supply container is outside the cell and connected to the processing apparatus by way of a comparatively long supply tube. Such an arrangement is especially unfavorable when the system is designed for simultaneous processing of two different connecting elements. On the supply unit, there is then a switch which guides the connecting element variant required in each instance for the next processing operation into the supply tube. If for reasons of control the call for the next connecting element is transmitted to the supply unit very late, undesirably long cycles result from the long supply tube.
EP 0,922,538 B1 discloses a method in which a connecting element in the form of a self-piercing rivet having a head and a shank offset from the head is supplied by a supply unit through a passage of a loading device arranged at the self-piercing riveter. The passage has a T-shaped cross-section, substantially corresponding to the projected area of the rivet. The rivet is here supplied to the passage with longitudinal axis directed transverse to the direction of travel, and individually transported through the passage to the loading device by means of air. In the direction of loading, the self-piercing rivet supplied is braked and held in an initial position suitable for the operation with the aid of movable positioning segments and a locking element. This known method and the devices disclosed in the document for the purpose have proved successful in practice. In the case of rapid cycles and long transmission routes, however, the duration of direct individual supply of connecting elements by the supply unit proves disadvantageous.
In a method disclosed by EP 0,511,093 B1 for conditioning and delivering small cylindrical parts, such as screws or rivets, the parts are arranged in the same direction, with the shank forward, in a column in a cylindrical supply tube, provided at the top with an opening for feeding with parts and a compressed air entrance and an exit below, associated with a means for intermittent delivery of the parts. The cylindrical tube is annularly arranged in several turns inside a rigid container forming a magazine in which a large number of parts are stored. The inside diameter of the tube is greater in a certain ratio than the greatest diameter of the parts, so that a stream of air by which the parts are driven ahead towards the exit along the tube can flow past the parts to the exit end. This known method has the disadvantage that it requires a comparatively large space near the processing apparatus. Besides, the energy required to transport the parts is relatively large, since in each delivery of a part, the entire column of many parts must be moved. Short-time exchange between parts of different lengths is not readily possible.
A device for supplying rivets to a self-piercing rivet tongs is disclosed by DE 10,064,241 A1. In this known device, the rivets are singly arranged one behind another in a tubular magazine, the magazine being acted upon by compressed air and so dimensioned that a small stream of compressed air can flow past the rivets towards the anterior end of the magazine. At the anterior end of the magazine, there is a means of rivet individuation and delivery consisting of a slide having a rivet-receiving opening slidable to and fro on the tongs transverse to the principal extent of the magazine between a first position for accepting a rivet from the magazine and a second position for delivering the accepted rivet to the tongs. To remove the rivet from the opening of the slide, it is acted upon in the second position of the slide by compressed air, advancing the rivet into a rivet-receiving opening of the tongs and holding it there by negative pressure generated at the anterior end of the ram by way of a bore through it. After transfer of the rivet, to perform a riveting operation the tubular magazine and the means of individuation and delivery pass from a rivet delivery position into a riveting position, in which the head of the rivet tongs is exposed. This known device is costly. A short-time exchange between two rivet versions is not possible.
The object of the invention is to specify a method of the kind initially mentioned that makes possible the feeding of the connecting elements to a processing apparatus in a short time and distinguished by a reliable and trouble-free mode of operation. It is also to be possible to supply at least two different connecting elements within a short time. Another object of the invention is to create a device suitable for operation of the method.
In the method according to the invention, the conveyance of the connecting elements takes place in two steps separate from each other, a first conveyance step in which the connecting elements are individually conveyed from a supply unit into an intermediate reservoir in the neighborhood of the loading means, and a second step in which an individual connecting element is conveyed from the intermediate reservoir into the loading device of the processing unit, at least two like or unlike connecting elements being picked up from the intermediate reservoir, and an arbitrary one of the connecting elements picked up from the intermediate reservoir, being selected and supplied by the process in the second step. By the method according to the invention, the supply time governing the cycle is considerably reduced, so that only the second step has an effect on the length of the cycle, and the period of the second step, owing to the arrangement of the intermediate reservoir on the processing unit near the loading means, is extraordinarily short. Even with delayed supply commands, a short timing can be realized. The first step in the method according to the invention expediently occurs depending on the fill level of the intermediate reservoir, i.e. immediately in each instance when the execution of a second step withdrew a connecting element from the intermediate reservoir. There is then enough time available to refill the emptied storage space, since the first step can be executed simultaneously with a processing step, the disadvantage of a long conveyance passage is therefore no longer a problem, and a late call for the second step is actually of advantage to the available time window.
The method according to the invention has the further advantage that with at least two different connecting elements, the order in which the several connecting elements are supplied to the processing unit may be random, and the connecting element variant to be supplied need not be determined until just before initiation of the second step. Since the intermediate reservoir at any time contains only one connecting element of each variant to be supplied, it may be of comparatively light and compact construction. The interference contour and weight of the processing unit are therefore not especially encumbered by the intermediate reservoir.
The device for supplying connecting elements to a processing unit, according to the invention, comprises an intermediate reservoir preceding the loading device of the processing unit, arranged to accommodate at least two connecting elements supplied through the passage and having at least two storage chambers, each having an entrance opening and an exit opening, the segment of the passage leading to an arbitrary one of the entrance openings and the segment of the passage leading to the loading device being connectable to an arbitrary one of the exit openings. Owing to the conformation according to the invention, each storage chamber of the intermediate reservoir can be supplied with a connecting element via the passage in any sequence, and any one of the stored connecting elements can be taken from a storage chamber and supplied to the operating unit. Preferably the intermediate reservoir is configured to accommodate at least two different connecting elements, for example of different lengths. The connection desired in each instance between the entrance and exit openings and the segments of the passage associated with them can be effected for example by a slide control, in which the passage openings are moved relative to the openings of the storage chambers. Another possibility consists in that switch-controlled branchings or passage segments movable relative to the chamber openings are arranged between the chamber and the passage openings.
In a preferred embodiment of the intermediate reservoir, according to the invention, the storage chambers are arranged side-by-side in a chamber housing, the entrance openings and the exit openings being located on opposed sides of the chamber housing and the chamber housing being movable to and fro between two placements in a housing, a first chamber and a second chamber being connected with the connecting openings provided for the passage in the housing of the intermediate reservoir. This conformation of the intermediate reservoir is simple and inexpensive to produce, and ensures a reliable mode of operation. To move the chamber housing, preferably a double-action pneumatic cylinder is provided.
Another contribution to the simplification of the intermediate reservoir is that the entrance opening and the exit opening of a reservoir chamber are connectable simultaneously to the associated segment of the passage in each instance. So that a connecting element supplied to the intermediate reservoir can here be held back in the intermediate reservoir, the exit opening is closable by means of a controllable barrier, preferably arranged in the housing of the intermediate reservoir. To actuate the barrier, a double-action pneumatic cylinder may be provided. The chamber housing may advantageously be configured as a slide of rectangular shape, lodged movable lengthwise in a prism-shaped opening in the housing of the intermediate reservoir and penetrated by the storage chambers transverse to its direction of motion. It is expedient further if, in the storage chambers behind the entrance openings in the direction of conveyance, latches are arranged that permit a motion of the connecting elements in forward direction and block it in the opposed direction.
To convey the connecting elements located in the intermediate reservoir to the loading device, a nozzle opening into the passage may be provided for the supply of blown air in the housing of the intermediate reservoir, and be so arranged that the jet of blown air leaving the nozzle is directed into the entrance opening of the storage chamber connected to the passage at the time. This conformation has the advantage that no blown air openings are required on the movable chamber housing. Besides, with the help of this blown air supply, the motion of supplied connecting elements passing the latch can be supported, and any connecting elements can be prevented from getting stuck in the vicinity of the latch.
So that the presence of connecting elements in the storage chambers can be monitored, sensors are arranged on the storage chambers whose signals serve to control the supply of connecting elements and the individual steps. As an alternative, sensors may be arranged in the connection openings, which produce a signal when a connecting element passes through. Other sensors detecting when a connecting element leaves the supply unit are preferably provided on the latter. These sensors make possible a simple and reliable control of the supply process and an early recognition of trouble. As sensors, electromechanical, electromagnetic and optical sensors are available.